Low tension surface discharge spark plug



April 21, 1959 W. B. SMITS 3,

LOW TENSION SURFACE DISCHARGE SPARK PLUG Filed May 28, 1954 INVENIOR.

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United States Patent LOW TENSION SURFACE DISCHARGE SPARK PLUG Wytze Beye Smits, Voorburg, Netherlands, assignor to Smitsvonk N.V., Leidschendam, Netherlands, a com- P y Application May 28, 1954, Serial No. 433,171

3 Claims. (Cl. 313-131) This invention relates to a low tension surface discharge spark plug and in particular to an arrangement for joining the electrode assembly to the spark plug body.

In spark plugs of this type the electrode assembly comprises essentially two concentric electrodes spaced from each other by a non-conductive or semi-conductive layer. In operation the spark burns with great intensity across the semi-conductive layer at the point of least resistance and tends to burn away the layer at that point.

Since failure of the spark plug is due almost entirely to the complete burning away of the semi-conductive layer, it would be advantageous to construct a plug in which the electrode assembly, including the layer, is easily.

removable from the main body of the plug, and thus replacea'ble when it becomes worn out.

In attaining the replaceability feature certain requirements must be met. In considering these requirements it must be understood that the life of the plug depends upon the burning of the semiconductive layer taking place uniformly around the circumference of the layer and therefore it is most important that the resistance between the electrodes at all points be substantially the same. Consequently, the spacing between electrodes is critical. Thus the first and perhaps most important consideration is that the means for attaching the electrode assembly to the main body of the plug must be such that the critical spacing between the electrode will not be altered during the replacing operation.

Second, the possibility that the attaching means might become loose and drop into the combustion cylinder must be avoided.

Third, it is advisable that the replacement of electrode assemblies requires no special tools or unusual abilities.

The object of the invention is to provide a spark plug which meets these requirements and to provide a spark plug with a replaceable electrode assembly.

It is another object of the invention to provide an arrangement by which the electrode assembly may be replaced without requiring special skills or tools, and without damage to the critical electrode spacing.

it is still another object of the invention to provide means for attaching the electrode assembly to the spark plug, which means are operable from the side of the plug remote from the combustion chamber, whereby no attaching parts will be exposed to combustion and will not accidentally drop into engine cylinders.

It is another object of the invention to attach the electrode assembly to the main body of the spark plug in such a way as to provide the greatest heat dissipation from the electrode assembly.

These and other objects of the invention will become more readily apparent Lirom the following detailed description of the invention taken in conjunction with the accompanying drawings in which,

Fig. 1 is an elevational view partly in section showing a spark plug embodying my new invention, and

Fig. 2 is a fragmentary cross sectional view of an alternative embodiment.

the lowermost surface of the metallic member 1.

The spark plug according to the invention is characterized by a centrally located spindle attached to one end to the electrode assembly and at the other end to the end of the spark plug remote from the electrode assembly.

As shown in Fig. l, the spark plug consists of a metallic member 1 having screw threads 2 in the lower end thereof for fastening to an engine block or the like, and hexagonal surfaces 3 for engagement by a spark plug wrench. A metallic bushing 6 is located through the center of the member 1 and is held in place by insulator 5 and a high temperature resisting insulating material 4 which is pressed inside member 1. A gas tight seal is thus formed between member 1 and bushing 6.

A spindle 7, threaded at both ends is fitted snugly in bushing 6 and the electrode assembly 8 is threaded on the lower end of the spindle. It is to be understood that the electrode assembly 8 could be attached to the spindle by other means or could be permanently fixed to the spindle, however, the illustrated embodiment has been lfound to be most practical.

The electrode assembly consists of an outer ring shaped electrode 14, an inner ring shaped electrode 15 and insulation 16 separating the electrodes. An insulating or semi-conducting layer 17 forms the outer or active surface of said insulation, and it is the layer 17 which supports the spark discharge.

A very thin copper sealing ring 9 is disposed around the spindle between the electrode assembly and the lower end of bushing 6. An asbestos ring 10 is located between the electrode assembly and insulating material 4 to assure proper seating of the electrode assembly even though there may be irregularities in the mating surfaces of the electrode assembly and insulating material.

Screwed to the end of the spindle 7 remote from the electrode assembly are nuts 12 and 13 which serve to tighten and retain the electrode assembly in place. A second copper sealing ring 11 similar to ring 9 is located between nut 12 and bushing 6.

When assembling the spark plug, the spindle 7 is pushed in from the underside of the bushing 6 and the copper sealing rings 9 and 11 are jammed against the bushing 6 and spindle 7 at either end to form gas tight seals between these members.

From the above it will be evident that the construction according to this invention is very simple and that for the replacement of the electrode assembly 8, only the nuts 12 and 13 need to be removed, whereafter the spindle 7 with the electrode assembly can be dismounted. Further, it should be evident that the attaching of the electrode assembly to the spark plug body can be effected without the use of tools on the electrode assembly itself, thereby avoiding the possibility of altering the spacing between the electrodes.

Theembodiment shown in Fig. 2 is particularly advantageous in operations which subject the spark plug to unusually high temperatures. As shown in Fig. 2, the sparking surface of the electrode assembly is flush with In this position, the [118131106 between the semi-conductive layer 17, and the metallic member 1 is considerably shorter than the distance between these elements as shown in Fig. l. Obviously, the heat dissipation from the semiconductive layer and the surrounding electrodes will be much greater in the embodiment of Fig. 2.

In a general manner, while there has been disclosed in the above description what is deemed to be the most practical and efficient embodiment of my invention, it should be well understood that the invention is not limited to such embodiment as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as 55' comprehended within the scope of the accompanying claims.

I claim:

1. A low tension surface discharge spark plug comprising, in combination, a bodyfor said plug comprised mainly of insulative material and having an outer metallic portion, said insulation circumscribing a longitudinal hole therethrou' a metallic bushing inserted in said hole, said insulation constituting a gastight seal between said 'bushing and the outer metallic portion of said body, a

unitary sparking element, comprising two concentric eiectrodes separated by a semi-conductive medium, and disposed on a spindle so as to be interchangeable therefrom, said spindle inserted in said hole so as to leave said sparking element seated axially with said insulation and bushing and circumscribed by said outer metallc portion, a sealing ring separating said sparking element from said bushing and an insulating ring separating said element and said body insulation so as to leave an air free juncture among said respective parts,'and said spindle having means at its tEree end for securing its position within said hole and for maintaining a pressure tight fit among said respective parts.

2. A spark plug according to claim 1 having a second sealing ring clamped between said bushing and said means.

3. A spark plug according to claim 1 wherein said securing and maintaining means comprises at least one nut screwed on the free end of said spindle.

References tCited in the file of this patent UNITED STATES PATENTS 1,032,099 Zahringer July 9, 1912 1,272,954 Homing July 16, 1918 2,135,297 Vila Nov. 1, 1938 2,483,357 Winholm Sept. 27, 1949 2,578,754 Smits Dec. 18, 1951 2,684,665 Tognola July 27, 1954 FOREIGN PATENTS 724,211 Great Britain Feb. 16, 1955 

